physical vapor transport (pvt) growth · physical vapor transport (pvt) growth (with focus on sic...

15th International Summer School on Crytsal Growth – ISSCG -15

Physical Vapor Transport (PVT) Growth (with focus on SiC and brief review on AlN & GaN)

Peter J. WellmannCrystal Growth Lab, Materials Department 6

University of Erlangen, [email protected]

15th International Summer School on Crystal Growth – ISSC G-15 WELLMANN, Peter – vapor growth

SiC – wide bandgap semiconductorEg=2.3eV...3.3eV (Si: Eg=1.1eV)

power & high frequency electronicsSiC with high

break-down voltage (10 x Si)heat conductivity (3 x Si)e– saturation velocity (2 x Si)

� applications: computer power supplywithout cooling parts

SiC Schottky diodes with low switching losses

Application Field of Silicon Carbide

blue opto-electronicsn-SiC substrate

(InGaN-based LEDs und LDs)


Application Field of Silicon Carbide

chemically resistent� sensors in „aggressive“ environments � automobile gas sensor

„visible blind“ photo diodes� sensors: temperature measurement in ovens, UV-exposure, ...

x-ray & γγγγ-ray detectors

bio-compatible� coatings of implantation parts in medicine

© S-SENCE,Sweden

© Istituto Nazionaledi Fisica Nucleare (INFN)

Trento, Italien


SiC Polytypes4H-SiC 6H-SiC 3C-SiC

Bandlücke [eV] 3,265 3,023 2,390

Gitterparameter[Å]

a = 3.08c = 10.05

a = 3.08c = 15.12

a = 4.36

Eff. Masse [me] me = 0.37mh = 0.94

me = 0.69mh = 0.92

me||/⊥ =0.68/0.25

Bewegl. µT=300K cm2/Vs]

µe = 500µh = 50

µe = 300µh = 50

µe = 900µh = 20

4H-SiC6H-SiC

Eg=2.4eV

Ec=2.4eV

Ec=0eV

3C-SiC

Eg=3.0eV

Ec=3.04eV

Ec=0.04eV

6H-SiC

Eg=3.0eV

Ec=3.05eV

Ec=0.05eV

15R-SiC

Eg=3.2eV

Ec=3.27eV

Ec=0.07eV

4H-SiC

Eg=3.3eV

Eg=3.43eV

Eg=0.13eV

2H-SiC

Hexagonality 0% 33% 40% 50% 100%


SiC crystal growth processPVT = physical vapor transport


Phase diagram of SiC

T1<T2

T

z

Ttop, Pcoil, pArgon

PVTPhysical Vapor TransportSUBLIMATION SiC powderCRYSTALLIZATION at colder seed

0 20 40 60 80 100

0

1000

2000

3000

4000

T [°

C]

carbon [at%]

SiC+C

Si+SiC

L+SiC

L+C

G+CG

L

L+G

Peritecticum(≈ 13% C)

2830°C±40°C

1414°C


8hgraphitization/powder consumpt.

40h

2h

0hSiC crystal

Graphite crucible

SiC source

1h

formation ofdisk

15h

X-ray source

Patent with SiCrystal AG, DE 199 15 473.2-51Wellmann, Straubinger and Winnacker.

Wellmann et al. JCG 216 (2000) & JCG 275 (2005).

Digital x-ray imaging – insitu visualization of SiC PVT growth


global PVT growth process

t=15h

graphitedust ?→C inclusions

mass transferlimitationby diffusion

δδδδT/δδδδx drop at disk(stable needle like surface)

SiC crystal

SiC source

SiCcrystal

SiC source

crystallization(kinetics)sublimation

diffusion

disk-like structure

heatdissipation


review on SiC crystal growth (historic remarks)


SiC crystal growth – a little bit of history

Acheson technique (today e.g. for SiC polishing powder applications)

greatcurrent

graphite

SiO2/C-powder

SiC

druse

T = ca. 1800°CSiO2 + 2C � Si + 2COSi + C � SiChighly Al-contaminated


SiC crystal growth – a little bit of history

Lely technique (SiC platelets) T=2200°C...2800°Cinert gas = Argonpressure = ca.1000mbar

SiCplatelets

porousgraphite

SiC powder


SiC crystal growth – a little bit of historyTairov & Ziegler technique (modyfied Lely ~, seeded sublimation)

T=2200°C...2400°Cinert gas = Argonpressure = ca. 15mbar...50mbar

SiC seed

SiC powderporous graphite


mass transport model& gas phase composition

• chemistry

• mass transport • simple PVT model


© Selder, JCG 211 (2000)

Fundamental of PVT Growth 1• Sublimation & Gas Phase Composition

© Lilov, 1995

I,

II,

III,


Fundamental of PVT Growth 2• SiC Deposition (assumption: no silicon droplets or carbon inclusions)

• Kinetic Side Wall Reactions (experiment: no Si or SiC deposition)

• T-field, Partial Pressures & Mass Transport Driving Force � Super-Saturation,

© Selder, JCG 211 (2000)


Fundamental of PVT Growth 3• Diffusion limited growth mode

• “Convection” issues© 1D-model, St. Müller, Dissertation Erlangen 1995


application of numerical modeling for process optimization


In-Situ Growth Control Tools

Numerical Modeling of T-fieldstate-of-the-art

Temperature Measurementstate-of-the-art

SiC powder

SiCseed

pyrometer

pyrometer

In-Situ X-ray VisualizationWellmann et al. (ICSCRM1999)

X-ray source

SiC crystalGraphite crucible

SiC source

In-Situ X-ray DiffractionYamaguchi et al. (ICSCRM1999)Konias et al. (ECSCRM2006)Wellmann et al. (ECSCRM2008)


Numerical ModelingTemperature field• Inductive heating• heat transfer by

• conduction• radiation• convection

Hofmann et al. J.Cryst.Growth (1995)Pons et al. J.Electrochem.Soc. (1996)

Mass transport - crystal growth• mass transport by diffusion and

convection• heterogeneous chemical reactions of

Si- and C- containing gas species with crucible etc.

• sublimation: SiC+C system (graphitization)

• crystallization: SiCSelder et al. J.Cryst.Growth (2000)

sketch PVTgrowth cell

T-field (3h) &mass transportpaths

SiC powder

SiCseed


SiC source material – granule core-shell model

Evolution source material

granular morphology - spheres• mean granular radius r• porosity ε• SiC core r• graphite shell r-rcore• graphitization γ = 1-(rcore/r)3

sublimation / recrystallization• C-shell porous for Si-C vapor• co-existence SiC & C• constant granule concentration

species transport in SiC source• convection & diffusion

Kulik et al., Mat.Sci.Forum 2004.Virtual Reactor Sofware,© SoftImpact Ltd.

Porosity ε after 3h Graphitization γ after 3h

SiSi2C

SiC2

Si-Cvapor


Doping


Doping of SiC – overview dopants

Leitungs-band

Valenz-band

NP

AlAkzeptoren

Donatoren

6H-SiC

(1100)(0120)

(000

1)

N(V) auf C(IV)-Platz

P(V) auf Si(IV)-Platz

Al(III) auf Si(IV)-Platz

Er(3+) auf Si(IV)-Platz

C(IV)

Si(IV)

(1120)


Doping of SiC – “Face”-competition effect

Al NSi-face

AlN

C-face


Modified-PVT – process principle

Al

doping species(i.e. N, P, Al , ...)

T1<T2

T

x

sourcedepletion

continuousdopantsupply

only gasesinert tographite(T>2000°°°°C)

... solid source ... additionalgas pipe

Doping by... gas supply

PVT setup

dopant gas(i.e. N2)

M-PVT setup

Straubinger, Wellmann et al. JCG 240 (2002)Wellmann et al. JCG 275 (2005)

n-type SiC:Np-type SiC:Al


Defects


Defects in SiC – 0-dim (point defects)

INTRINSICe.g. Si-Vacancy

as well as related complexesC-Vacancy, CSi Antisite

EXTRINSICunintentional doping!e.g. Ti, B, N


Defects in SiC – 1-dim (Dislocations)revealed by KOH-defect etching & light microscopy

p-type

p=3⋅⋅⋅⋅1017cm -3

Screw Dislocations

EdgeDislocations

p=2⋅⋅⋅⋅1019cm -3

n≈≈≈≈2⋅⋅⋅⋅1017cm -3

“Basal-Plane”Dislocations

n-type

x3 x2

φα

br

Ix3 x2

φα

brx3 x2

φα

br

I© Mark Ramm

x2

br

x3

α=φ

IIIx2

br

x3

α=φ

x2

br

x3

α=φ

III

“Basal-Plane”Dislocations

Screw orEdgeDislocations

Sakwe, Wellmann et al. JCG 289 (2006)


Defects in SiC – 1-dim (Dislocations)micropipes

density = 1cm-2 ... 50 cm-2

[000

1]

(0001)


Basal plane dislocations (BPDs) Dissociation & Stacking faults (SFs)

SF is formed from a 60°complete dislocation.

Twigg et al.APL vol. 82 (2003)

Deflected dislocation dissolves into two partial dislocations with a stacking fault in-between

Jacobson et al.JAP vol.91 (2002)

plane view

x3 x2

φα

br

Ix3 x2

φα

brx3 x2

φα

br

I© Mark Ramm

partial dislocationb=1/3·a � stacking fault

dislocation dissociation

© Blumenau, PhD-thesis 2002. (here: cubic lattice)

side view


TEM: Collaboration Prof. Strunk (Materials Science 7, Uni-Erlangen)

© Iwata et al. J.Phys.Cond.Matt. 2002.

100nm

gliding directionSFs

[0001]

Basal-Plane Dislocations& Stacking Faults

8° off oriented (0001)n-type 4H-SiC

“Basal-Plane“ Dislocations � Stacking Faults


Defects in SiC – 2-dim(Stacking Faults, Polytype Changes)


Defects in SiC – 3-dim (Si-droplets, C-inclusions, hollow cores, also polytype inclusions)


Group-III-Nitrides

AlN � PVT

GaN � mainly HVPEInN � no bulk growth succeeded


PVT growth of AlN

Chemistry & crucible• Al + 1/2 N2 � AlN• tungsten crucible

challenges• purity AlN source (oxygen free)• small process window

Low T � needlesHigh T � decompositionIdeal = ca. 2200°C

• seedingcurrently often on 6H-SiCin future on AlN

© Crystal-N @ www.crystal-n.com© Bickermann, Epelbaum, Winnacker, Erlangen.


Heaters of 3-Zone Oven

Ga melt

N2/H2 + NH3

N2/H2 + GaCl3

AbgasN2/H2 + NH3

N2/H2 + HCl Susceptor &Substrate ( ↔↔↔↔)

Quarz TubeT=900°C T=1050°C

Hydrogenated Vapor Phase Epitaxy• great growth velocity

~ 50µm/h (Lit: ~100µm/h)• 6H-SiC Substrate

GaN HVPE growth process –


GaN Vapor Growth - HVPE

Lit: Ilegems, vapor epitaxy of GaN, J.Cryst.Growth 13/14 (1972), p.360.

Carrier:H, He or N2H-passivation of dislocations?

Ga-source:6HCl + 2Ga ↔ 2GaCl3 + 3H2Ga source @ 950°Cefficiency ~100%

N-source:NH3problem: formation of N radicals

Chemistry:2GaCl3 ↔ 2Ga3+ + 3Cl22NH3 ↔ 2N3- + 3H2Ga3+ + N3- ↔ GaNsubstrate @ 1050 °°°°C

„step flow“ instead of „3dim. nucleation“n = 2x1017cm-3

µ = 380 cm2/Vs

pyramidal growth with hexagonal symmetryn > 1018cm-3

NO GRWOTH

physical vapor transport (pvt) growth · physical vapor transport (pvt) growth (with focus on sic...

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